This invention relates to a vane compressor, and more particularly to a vane compressor which is light in weight and free from seizure of its component parts and also has improved fluid tightness between the suction side and the discharge side in the pump housing.
A vane compressor in general has a pump housing which is formed by a cylinder in which a rotor carrying vanes is fitted in concentricity therewith, and two side blocks secured to the opposite ends of the cylinder. The combined weight of the pump housing and the rotor occupies the greater part of the total weight of the compressor. Therefore, one would easily consider a vane compressor can be lighter in weight if it has its pump housing and rotor formed of aluminum or an alloy thereof (hereinafter called "aluminum metal"), like other types of compressors.
However, the vane compressors have the following peculiar problems, which currently necessitates manufacturing vane compressors which have only vanes formed of aluminum metal but have a pump housing and a rotor formed of iron or an alloy thereof (hereinafter called "ferrous metal"):
First, a vane compressor has many frictionally contacting portions, e.g. those between the rotor and the vanes, between the vanes and the cylinder and between the rotor and vanes and the side blocks. If two frictionally contacting parts are both formed of aluminum metal, seizure will easily take place between them, since aluminum metals are apt to adhere together when heated.
Secondly, in view of the vane compressor arrangement that compression chambers, which are defined by adjacent vanes, the rotor and the pump housing, are repeatedly expanded and contracted alternately to carry out fluid compressing action, the clearances between the rotor and the cylinder and between the rotor and the side blocks have to be kept at very small values with accuracy to obtain fluid-tightness between the suction side and the discharge side in the pump housing as well as minimize the friction resistance of the moving parts. However, if one of two contacting parts is formed of aluminum metal and the other ferrous metal, the clearance between these parts cannot be maintained at its proper value due to heat produced during operation of the compressor, because aluminum metals generally have much larger coefficients of thermal expansion than ferrous metals.
This problem is particularly serious at opposite sealing portions located between the inlet ports and the outlet ports of the cylinder, at which the rotor and the cylinder are disposed in contact with each other in a manner keeping fluid tightness between the suction side and the discharge side in the pump housing. The clearance between the rotor and the cylinder at these sealing portions should have a very small value of the order of 0.01-0.04 mm to minimize the leakage of fluid from the discharge side to the suction side on one hand, and to minimize the friction resistance between the rotor and the cylinder caused by rotation of the former on the other hand. To satisfy both of these two incompatible requirements, conventionally the clearance between the rotor and the cylinder at the sealing portions was set at the above small values. This required machining the rotor and the cylinder with very tight outer diameter and inner diameter tolerances, respectively. Further, abrasion of the rotor and the cylinder which proceeds with the operation of the compressor causes a gradual increase in the clearance between the two members at the sealing portions, resulting in a drop in the compression efficiency and a shortened life of the compressor.